(1967, Don Knotts, Leslie Nielsen)

Knotts travels twice by Greyhound, and two PD-4501 Scenicruisers appear.
On the first occasion, he boards this one, with fleet number 1518 on the front and with 'Tulsa' as its destination:

He gets off this one, fleet number 1172 with 'Houston' as its destination. Note this one has the number B223 over and inside the door:

On the second occasion, it's again 1518, again with 'Tulsa' as the destination. Look closely and you'll see two separate sequences were filmed with this bus. This time we see inside it as well.